The present invention relates to amplitude phased keyed communications systems, and more particularly, to an improved amplitude phased keyed digital symbol recovery circuit for use in an amplitude phased keyed digital communications system.
In conventional communication systems, adaptive digital symbol recovery is performed by analog threshold processing of I and Q baseband signals. Any signal can be decomposed into orthogonal signals comprising in-phase (I) and quadrature (Q) signals. In amplitude phase keyed (APK) communications signals, the transmitted symbols arc typically recovered via sum and difference circuits operating on the orthogonal signals at baseband. With the knowledge of the amplitude of each of the signals at the correct sample times, amplitude phase keyed symbols can be recovered. However, conventional communication systems are not expandable nor programmable. Conventional communication systems typically do not process a very wide variety of signal constellations and cannot be programmed to process new signal constellations using only a memory upload sequence.
False lock detection is conventionally done by monitoring the bit error rate of the system, which typically involves the use of added circuitry. Therefore, false lock detection is relatively complex and costly to implement. Carrier lock status is conventionally implemented using a complex circuit configuration, and is also relatively costly to implement.
Therefore, it is an objective of the present invention to provide for an amplitude phased keyed digital communications system having an improved digital symbol recovery circuit. It is a further objective of the present invention to provide for an amplitude phased keyed digital communications system having an improved digital symbol recovery circuit that is programmable and expandable and that provides a means for cost-effectively implementing carrier tracking and recovery and false lock detection, automatic gain control and that is capable of processing a wide variety of signal constellations using only a memory upload sequence to adapt to the new signal constellation.